The present invention relates to a method and apparatus for performing a traffic measurement in a telecommunication network, like a public switched telephone network (PSTN) or a public land mobile network (PLMN).
An understanding of the nature of the telephone traffic and its distribution with respect to time and destination is essential in determining the amount of telephone facilities required to serve the subscribers"" needs.
The telephone traffic is defined as the aggregate of telephone calls over a group of circuits or trunks with regard to their durations of the calls as well as there numbers. Traffic flow through a switch or trunk group is defined as the product of the number of calls during a period of time and their average holding times. In traffic theory, the unit of time is one hour. Let C be the number of calls originated in one hour, and T be the average holding time, then the traffic flow intensity A is calculated on the basis of the following equation:
A=Cxc3x97T
For example, if there are 200 calls of average length of 3 minutes between Atlanta and Los Angeles in one hour, then the traffic intensity is:
A=200xc3x973=600 minutexe2x88x92calls
Expressed in hours, A=600/60=10. This value is dimensionless but a name was given to it. The international unit of telephone traffic is called xe2x80x9cerlangxe2x80x9d, named after the Danish mathematician A. K. Erlang, founder of the theory of telephone traffic.
From the example above, A=10 erlangs. This number represents:
1. The average number of calls in progress simultaneously during the period of one hour, or
2. The average number of calls originated during a period of time equal to the average call holding time, or
3. The total time, expressed in hours, to carry all calls.
In the US, the term Unit Call (UC) or its synonym xe2x80x9cCentium Call-Secondxe2x80x9d, abbreviated CCS is generally used.
To estimate traffic intensity, mechanical devices were invented to sample or observe the number of busy circuits. These devices can sample each trunk group once every 100 seconds (or 36 times per hour). If the measuring device found that in one hour, all 36 samples show that a particular trunk is being used, it is concluded that the trunk is being used the whole hour, thus by definition this trunk carries 1 erlang or 36 CCS (i.e. 1 erlang=36 CCS).
In the above example, if the average holding time is 5 minutes instead of 3 minutes, then the traffic intensity is:
A=(200xc3x975)/60=16.67 erlangs
According to the above first definition, the average number of busy trunks between Atlanta and Los Angeles has just increased to 16.67 from 10, because the average subscriber holds a conversation 2 minutes longer
In a known traffic measurement performed for example in a fixed exchange switch of a PLMN, a sampling method is used. According to this method, traffic samples are taken continuously. The traffic intensity corresponds to the average value of these samples.
FIG. 2 shows a time diagram used for explaining the known traffic measurement.
It is assumed that the measurement starts at 12:15:00, wherein a result accumulation period is 15 minutes. The samples are shown and numbered in FIG. 2. In this connection, it is to be noted that sampling is running although measurement has not yet started.
The measurement is performed on the basis of counters for counting predetermined parameters used for calculating the resultant traffic. In the present case, counters are used for a current sample amount sa, an previous sample amount sap, an instantaneous load ld, a cumulative load lc and a previous cumulative load lcp.
At 12:15:00, the measurement starts and the counters are initialized. As call 1 is running, the instantaneous load amounts to ld=1. Since, according to FIG. 2, the measurement starts after 29 samples, the counters are initialized to a previous sample amount sap=29, a sample amount sa=29, a cumulative load lc=0 and a previous cumulative load lcp=0.
After the sample number 30, the counter are updated to ld=1, sap=29, and sa=30. The cumulative load lc is calculated on the basis of the equation lc=lc+ld=0+1=1.
At sample number 31, ld=1, sap=29, sa=31, lc=lc+ld=1+1=2.
Since call 2 starts at the time 12:18:00, the instantaneous load ld is increased to 2. Accordingly, at the sample number 32, ld=2, sap=29, sa=32, lc=lc+ld=2+2=4.
At sample number 33, ld=2, sap=29, sa=33, lc=lc+ld=4+2=6.
Since call 3 starts at the time 12:22:00, the instantaneous load ld is increased to ld=3.
Accordingly, at the sample 34, ld=3, sap=29, sa=34, lc=lc+ld=6+3=9.
At the sample number 35, ld=3, sap=29, sa=35, lc=lc+ld=9+3=12.
Since the call 3 is released at the time 12:27:00, the instantaneous load ld is decreased to ld=2.
Accordingly, at the sample number 36, ld=2, sap=29, sa=36, lc=lc+ld=12+2=14.
At the sample number 37, ld=2, sap=29, sa=37, lc=lc+ld=14+2=16.
At the time 12:30:00, 15 minutes after the start of the measurement, the first reporting is performed and the traffic intensity is calculated according to the following equation:
tr=(lcxe2x88x92lcp)/(saxe2x88x92sap)=(16xe2x88x920)/(37xe2x88x9229)=16/8=2
wherein tr denotes the calculated traffic in erlang.
After the above calculation, the previous sample amount is set to sap=37 and the previous cumulative load to lcp=16. In this respect, it is to be noted that the correct traffic value is 2.133 erlang. Thus, the calculation error is xe2x88x926.7%.
Until the second reporting at 12:45:00, the updating of the above counters is performed in the same manner as described above.
After the sample number 45, the following values are obtained: lc=30, lcp=16, sa=45 and sap=37.
Thus, the traffic intensity value amounts to tr=(30xe2x88x9216)/(45xe2x88x9237)=14/8=1.75 erlang. In the present case, the correct value is 1.667 erlang, such that the error amounts to +4.9%.
Thereafter, the previous sample amount is set to sap=45 and the previous cumulative load to lcp=30.
When the third report is issued at 13:00:00, the following values are obtained from the counters: lc=35, lcp=30, sa=50 and sap=45.
Thus, the traffic intensity value amounts to tr=(35xe2x88x9230)/(50xe2x88x9245)=5/5=1 erlang. In this case, the correct value of the traffic intensity is 1 erlang, such that the error is 0%.
Thereafter, the previous sample amount is set to sap=50 and the previous cumulative load to lco=35.
When the fourth report is issued at 13:15:00, the following counter values are obtained: lc=40, lcp=35, sa=57 and sap=50.
Accordingly, the traffic intensity value amounts to tr=(40xe2x88x9235)/(57xe2x88x9250)=5/7=0.714 erlang. In this case, the correct traffic value is 0.667 erlang, such that the error is xe2x88x927.0%.
Thereafter, the previous sample amount is set to sap=57 and the previous cumulative load to lcp=40.
Accordingly, with this method of performing traffic measurement, the accuracy of the measurement as well as the load of a CPU performing the traffic calculation is obviously dependent on the sampling period. If the sampling period is short, accuracy and CPU load are both increased. However, if the sampling period is long, the accuracy will decrease so that short calls between samples will not be registered at all. In practice, a default sampling period is set to 36 seconds.
Another known method of performing traffic measurement is a time-based method used for example in a mobile exchange MSC (Mobile Switching Center) of a PLMN. This method is based on an object reservation time. A start time and a stop time of every call is stored. From these times, the total reservation time can be calculated. The traffic value or intensity is calculated by dividing the total reservation time by the accumulation period.
In the following, the time-based traffic measurement is explained on the basis of the call distribution shown in FIG. 2, wherein the measurement starts at 12:15:00 and the result accumulation period is 15 minutes.
At 12:13:00, the call 1 starts and the start time is registered.
At 12:15:00, the measurement starts and a previous report time is set to trp=12:15:00.
The call 2 starts at 12:18:00, such that the start time of call 2 is set to 12:18:00. Moreover, call 3 starts at 12:22:00 and a corresponding start time is registered for call 3.
At 12:27:00, the call 3 is released and a corresponding stop time of call 3 is registered. Moreover, since the call 3 has been released, a corresponding total reservation time or cumulative time tc is determined according to the equation:
tc=tc+(call 3 stop timexe2x88x92call 3 start time)=0+(12:27:00xe2x88x9212:22:00)=0+5 min=300s.
At 12:30:00, the first reporting and traffic intensity measurement is performed according to the following equation:
tr=(tcxe2x88x92tcp)/(trcxe2x88x92trp),
wherein tc indicates the current cumulative time, tcp the previous cumulative time, trp the previous report time and trc the current report time.
Thus, in the present case the traffic intensity value amounts to tr=(300 sxe2x88x920 s)/(12:30:00xe2x88x9212:15:00)=300 s/900 s=0.333 erlang. It is to be noted that the error is xe2x88x92640% (correct traffic value is 2.133 erlang), since only call 3 has been released in this measurement period.
Thereafter, the previous report time is set to trp=12:30:00 and the previous cumulative time to tcp=300 s.
At 12:40:00, call 1 is released and the corresponding stop time is registered.
Thus, the cumulative time amounts tc=tcoxe2x88x92(call 1 stop timexe2x88x92call 1 start time)=300 s+(12:40:00xe2x88x9212:13:00)=300 s+1620 s=1920 s.
In the second reporting at 12:45:00, the traffic intensity value amounts to tr=(1920 sxe2x88x92300 s)/(12:45:00xe2x88x9212:30:00)=1620 s/900 s=1.8 erlang. Thus, the error amounts to +7.9% (correct value is 1.667 erlang).
Thereafter, the previous report time is set to trp=12:45:00 and the previous cumulative time to tcp=1920 s.
The third reporting at 13:00:00 leads to a traffic intensity value tr=(1920 sxe2x88x921920 s)/(13:00:00xe2x88x9212:45:00)=0 s/900 s=0 erlang. Thus, the error is huge, since no calls were released in this measurement period at all.
Thereafter, the previous report time is set to trp=13:00:00 and the previous cumulative time to tcp=1920 s.
At 12:40:00, call 2 is released, the corresponding stop time is registered and the counter for the cumulative time is updated, such that tc=1920 s+(12:40:00xe2x88x9212:18:00)=1920 s+1320 s=3240 s.
The fourth reporting at 13:15:00 leads to a traffic intensity value of tr=(3240 sxe2x88x921920 s)/(13:15:00xe2x88x9213:00:00)=1320 s/900 s=1.467 erlang. In this case, the error amounts to +220%, since the correct traffic value is 0.667 erlang.
Thereafter, the previous report time is set to trp=13:15:00 and the previous cumulative time to tcp=3240 s.
As can be gathered from the above example, this known time-based method leads to the disadvantage that the calls are not registered until they are released. Moreover, calls are reserved before the measurement start will effect the traffic values.
Accordingly, both known methods and apparatuses for performing traffic measurement provide low accuracies and are not suitable for obtaining real-time traffic values.
Document JP-A-60 165160 discloses a method and apparatus for performing a traffic measurement as defined in the preambles of claims 10 and 14, respectively. In particular, a retention time measurement is performed at an exchange, wherein an operation start time and a release time of an individual telephone set is counted so as to calculate the retention time of the telephone set.
It is an object of the present invention to provide a method and apparatus for performing a traffic measurement, which provide exact and real-time traffic values.
This object is achieved by a method for performing a traffic measurement in a telecommunication network, comprising the steps of:
determining a cumulative total reservation time of a measurement object each time a traffic state of the object changes, and
calculating a traffic value by dividing a change of the determined cumulative total reservation time by a corresponding time period.
Furthermore, the above object is achieved by an apparatus for performing a traffic measurement in a telecommunication network, comprising:
means for determining a cumulative total reservation time of an object to be measured,
control means for controlling the determining means so as to update the cumulative total reservation time each time a traffic state of the object changes, and
calculating means for calculating a traffic value by dividing a change of the cumulative total reservation time by a corresponding time period.
Accordingly, since the cumulative total reservation time is determined each time a traffic state of the object changes, updating of the counters for calculating the traffic value can be done at any time regardless whether the traffic state of the object has changed or not. Thus, a correct cumulative total reservation time is always available such that exact and real-time traffic values can be obtained at any time of reporting.
Preferably, the calculation of the traffic value is performed when a traffic report is issued, wherein the corresponding time period is a time period since the last traffic report.
The total reservation time may be determined by multiplying a value of an instantaneous load by a time period since the last determination of the cumulative total reservation time, wherein the value of the instantaneous load is updated each time the traffic state of the object changes.
The traffic state change of the object may correspond to a call reservation or a call release.
Preferably, said object to be measured is an exchange switch.
Furthermore, the determining means may comprise a counting means for counting the instantaneous load, a previous updating time, a current time, the cumulative total reservation time, a previous cumulative total reservation time and a last report time, wherein the calculation means is arranged to read the counting means and to calculate the change of the cumulative total reservation time by subtracting a read value of the previous cumulative total reservation time from a read value of the cumulative total reservation time, and the corresponding time period by subtracting a read value of the last report time from a read value of the current time.
Preferably, the determining means determines the cumulative total reservation time by reading the counting means and by multiplying a read value of the instantaneous load by a difference between a read value of the current time and a read value of the previous updating time.
The counting means may be updated, when a traffic report is requested.
Furthermore, a clock system may be provided for supplying a clock and for notifying the counting means of a clock change.
Further preferred developments of the present invention are defined in the dependent claims.